Republicans vowed Thursday to push further against findings by the Interior Department's internal watchdog that the Obama administration's changes to a study of the jobs impact of a potential rule on mining pollution were not politically motivated.

At issue at the House Natural Resources Committee hearing was whether the Obama administration forced a contractor to reconfigure calculations for a possible rule protecting streams from pollution from mountaintop-removal mining, a controversial practice, to reduce the number of job losses.

The Obama administration hasn't yet floated a new rule protecting streams from mountaintop-removal mining, a process in which mining companies blast away peaks and push debris into valleys to access coal seams. Known as the Stream Buffer Zone Rule, the administration moved to issue its own rule after a 2008 version of the law approved under former President George W. Bush was challenged in court.

"There was no evidence that there was political motivation," said Robert Knox, assistant inspector general for investigations for the Interior Department.

Committee Chairman Doc Hastings, R-Wash., vowed to use the full powers of the panel — including issuing subpoenas for more information — to further assess whether political influence played a role.

"I don't think this issue is going to go away," he said.

Many Democrats, as well as environmental groups, want to see the rule go forward. They say it would enhance water quality and improve health for Appalachian communities where the mining method is practiced, as well as for people who live downstream.

"I would like to know why there isn't a new rule and when are we going to see a new rule," said ranking member Rep. Peter DeFazio, D-Ore. "But none of that is before us today."

Republicans say the rule would cost jobs in the mining industry, stunting activity near waterways. Given some of the other regulations coming from the Obama administration that seek to reduce the use of coal, they were unconvinced Thursday that the alteration in the environmental analysis was devoid of political motivation.

"We might tend to disagree on that," Rep. Scott Tipton, R-Colo., responded to Knox's assertion that there was no political motivation. "It does appear as if they were attempting to cook the books on this."

Republicans have charged that foul play was involved, suggesting the Office of Surface Mining Reclamation and Enforcement instructed the contractor performing the review to use the 2008 law instead of the older 1983 version as the baseline for its formula for determining job losses.

The initial estimate was 7,000 jobs, and the subsequent one was lower — though that total has not been released.

The investigation is attracting attention in the Senate as well, as a bipartisan group of senators sounded off on the report Wednesday.

"Neither OSM nor any other agency should rig the method by which costs and benefits are estimated in order to achieve a politically desired outcome. Such actions violate federal law and must not be allowed to take place," Sens. John Barrasso, R-Wyo., Mike Lee, R-Utah, Rob Portman, R-Ohio, and Joe Manchin, D-W.Va., said in a letter to Janice Schneider, Obama's nominee for assistant secretary for land and minerals management at Interior.

At the hearing, Knox said the investigation did not attempt to assess the accuracy of the 7,000 figure, but noted that the processes used to arrive at it and the lower estimate were acceptable.

Still, Knox noted that the changes came late and that the contractor had "limited experience" and "would have undertaken different techniques if they had more time."